Although formed continuously, glass is typically segmented into sheets as soon as it has cooled and solidified. Recent product trends have resulted in requirements for thinner glass. As glass thickness decreases, the sheets and the ribbons from which they are cut become more flexible. This flexibility creates a challenge from a handling perspective, particularly for glass thinner than 0.3 mm.
Glass has a number of unique features that make guiding a glass ribbon particularly challenging. First, the glass is extremely sensitive to surface defects. These defects create stress points that generate cracks and lead to breakage. Thus, direct contact with the glass surface, as is typically done to edge-guide a plastic, paper, or metal web, must be done in a way that minimizes the forces on the glass. Second, when subject to lateral forces, a thin glass ribbon can buckle and eventually break. In contrast, polymer films and paper webs are more compliant and thus respond better to lateral forces.
Third, the ribbon-forming process can produce variations in the thickness of the ribbon across its width, as well as “camber” in the motion of the ribbon. FIG. 1 illustrates a glass ribbon 13 which exhibits camber 10 (greatly exaggerated in this figure for purposes of illustration). As can be seen, camber is a continuous curvature of the ribbon in one direction (i.e., to the right in FIG. 1). Such curvature can be caused by, for example, different rates of cooling of a ribbon's edge beads. Camber, thickness variation, and residual stresses in the glass ribbon can cause the ribbon to shift laterally, rather than conveying in a straight line.
These unique features of glass ribbons make conveying and winding of ribbons of thin glass more challenging than conveying and winding of flexible webs in the plastic, paper, and metal foil industries. In these other industries, guiding of a web is typically accomplished by using fixed edge guides that rub against the web's edges. Experiments have shown that these techniques are a complete failure when applied to thin glass ribbons because they cause the ribbon to break.
A solution to the guiding problem for thin glass ribbons would allow the ribbon to be wound in a continuous format and provided to users in that form. The users, in turn, could process the glass in the continuous format to make such products as ePaper front plane substrates, photovoltaics protective cover sheets, touch sensors, solid state lighting, solid state electronics, and the like. In general terms, continuous processing is advantageous both to the glass manufacturer and to the user. A need thus exists for effective methods of guiding thin glass ribbons. The present disclosure addresses this need.